1. Field of the Invention
The present invention relates to a liquid droplet jetting apparatus which jets liquid droplets.
2. Description of the Related Art
Conventionally, there are known ink jetprinters which jet ink droplets toward a recording medium such as a sheet of paper and the like to record an image and the like. Among the ink-jet printers, there have been those configured to be capable of selectively forming a plurality of types of dots different in size on the recording medium (gradation printing) by changing jetting amount of the liquid droplets jetted from one nozzle within a predetermined period (driving period). For example, Japanese Patent Application Laid-Open No. 2002-86766 (paragraphs 0007 and 0008, and FIG. 11) describes an ink-jet printer which applies any one of three types of driving pulses different in pulse width from each other to the ink-jet head in each predetermined period so as to jet a liquid droplet corresponding in size to the applied driving pulse.
Japanese Patent Application Laid-Open No. 2002-86766 describes that the landing positions on the recording medium may be deviated because the jetting velocities are different according to the sizes of the liquid droplets jetted from the nozzle. In particular, it is described that since a small liquid droplet tends to become lower in velocity than a large liquid droplet, landing positions of the small liquid droplets are deviated. Therefore, as a method for solving this problem, it is disclosed that in jetting the small liquid droplet, the timing for applying the drive pulse is advanced a little so as to apply the drive pulse for the small liquid droplet from the middle of the last period.
However, when the liquid droplet landing position are greatly deviated, little effect can be expected even if the drive pulse application timing is advanced to such an extent as only to overlap the last driving period.